1. Field of the Invention
The present invention relates generally to photographic cartridges, and more particularly to an optical-mechanical rotation sensing mechanism for a web-roll mounted for rotation within a cartridge.
2. Description of the Prior Art
Sensing mechanisms for sensing web rotation, or web transport, are well known in the prior art, as indicated in U.S. Pat. Nos. 3,564,219, No. 3,730,453, No. 3,779,483, No. 3,917,142, and No. 4,153,361.
Most of those patents utilize some type of sensing mechanism wherein pulses are generated for indicating a rotational velocity of the web spool. The pulses are fed to a counter, where they are accumulated, stored, and displayed to indicate the amount of web material remaining on the spool.
One problem with the prior-art sensing mechanisms is that, mechanically, they are of relatively complicated construction, which adversely affects the reliability and cost of such mechanisms. Another disadvantage of such mechanisms is that the web-roll cartridge normally interfaces with a printer or the like, and the optical-mechanical features of the mechanisms are normally mounted in the interfacing structure and not within the cartridge. That necessitates a larger and more complicated interfacing structure. The optical-mechanical rotation sensing mechanism of this invention is believed to eliminate these and other disadvantages of the known prior art.